Spectroscopic sensor including interference filter unit having silicon oxide cavity

ABSTRACT

A spectroscopic sensor 1 comprises an interference filter unit 20, having a cavity layer 21 and first and second mirror layers 22, 23 opposing each other through the cavity layer 21, for selectively transmitting therethrough light in a predetermined wavelength range according to an incident position thereof; a light-transmitting substrate 3, arranged on the first mirror layer 22 side, for transmitting therethrough light incident on the interference filter unit 20, a light-detecting substrate 4, arranged on the second mirror layer 23 side, for detecting the light transmitted through the interference filter unit 20, and a first coupling layer 11 arranged between the interference filter unit 20 and the light-transmitting substrate 3. The cavity layer 21 and the first coupling layer 11 are silicon oxide films.

TECHNICAL FIELD

The present invention relates to a spectroscopic sensor.

BACKGROUND ART

Known as a conventional spectroscopic sensor is one comprising aninterference filter unit for transmitting therethrough light having apredetermined wavelength according to an incident position of light, alight-transmitting substrate for transmitting therethrough the lightincident on the interference filter unit, and a light-detectingsubstrate for detecting the light transmitted through the interferencefilter unit. Here, a pair of mirror layers may oppose each other througha cavity layer so as to construct the interference filter unit as thatof Fabry-Perot type (see, for example, Patent Literatures 1 and 2).

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open No.2006-58301

Patent Literature 2: Japanese Translated International ApplicationLaid-Open No. H02-502490

SUMMARY OF INVENTION Technical Problem

When a resin material is used as a material for the cavity layer, acoupling layer arranged between the interference filter unit and thelight-transmitting substrate, and the like in the spectroscopic sensorsuch as the one mentioned above, however, the cavity layer, the couplinglayer, and the like may be degraded by changes in temperature, highhumidity, and the like of the environment where they are in use,

It is therefore an object of the present invention to provide a highlyreliable spectroscopic sensor.

Solution to Problem

A spectroscopic sensor in accordance with one aspect of the presentinvention comprises an interference filter unit, having a cavity layerand first and second mirror layers opposing each other through thecavity layer, for selectively transmitting therethrough light in apredetermined wavelength range according to an incident positionthereof; a light-transmitting substrate, arranged on the first mirrorlayer side, for transmitting therethrough light incident on theinterference filter unit; a light-detecting substrate, arranged on thesecond mirror layer side, for detecting the light transmitted throughthe interference filter unit; and a first coupling layer arrangedbetween the interference filter unit and the light-transmittingsubstrate; while the cavity layer and the first coupling layer aresilicon oxide films.

In this spectroscopic sensor, the cavity layer is a silicon oxide filmand thus can stabilize its form, light transmittance, refractive index,and the like more than when made of a resin material. The first couplinglayer is also a silicon oxide film and thus can stabilize thetransmission characteristic of the light advancing from thelight-transmitting substrate to the interference filter unit. The factthat the cavity layer and first coupling layer are silicon oxide filmscan also prevent their quality from being degraded by changes intemperature, high humidity, and the like of the environment where theyare in use. Hence, this spectroscopic sensor is highly reliable.

Here, the cavity layer may be a silicon oxide film formed by thermallyoxidizing silicon. This stably yields the cavity layer with high qualityat low cost.

The first coupling layer may be a silicon oxide film formed by a filmforming process using TEOS as a material gas. This can form the firstcoupling layer at low temperature and high speed with low stress, so asto prevent the cavity layer and first and second mirror layers frombeing damaged, whereby the cavity layer and first and second mirrorlayers are obtained with high quality.

The spectroscopic sensor may further comprise a second coupling layerarranged between the interference filter unit and the light-detectingsubstrate, while the second coupling layer may be a silicon oxide film.This can stabilize the transmission characteristic of the lightadvancing from the interference filter unit to the light-detectingsubstrate more than when the second coupling layer is made of a resinmaterial. The fact that the second coupling layer is a silicon oxidefilm in addition to both of the cavity layer and first coupling layercan more reliably prevent their quality from being degraded by changesin temperature, high humidity, and the like of the environment wherethey are in use.

The second coupling layer may be a silicon oxide film formed by a filmforming process using TEOS as a material gas. This can form the secondcoupling layer at low temperature and high speed with low stress, so asto prevent the cavity layer and first and second mirror layers frombeing damaged, whereby the cavity layer and first and second mirrorlayers are obtained with high quality.

The spectroscopic sensor may further comprise an optical filter layer,formed on the light-transmitting substrate so as to oppose the firstmirror layer, for transmitting therethrough light in the predeterminedwavelength range. This can make the light in the predeterminedwavelength range efficiently incident on the interference filter unit.

Advantageous Effects of Invention

The present invention can provide a highly reliable spectroscopicsensor.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a vertical sectional view of a spectroscopic sensor inaccordance with an embodiment of the present invention;

FIG. 2 is a plan view of a cavity layer in the spectroscopic sensor ofFIG. 1;

FIG. 3 is a vertical sectional view for explaining a method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 4 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 5 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 6 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 7 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 8 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 9 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 10 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 11 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 12 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 13 is a vertical, sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 14 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 15 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 16 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 17 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 18 is a vertical sectional view for explaining the method formanufacturing the spectroscopic sensor of FIG. 1;

FIG. 19 is a profile chart illustrating the relationship between aresist layer and the cavity layer;

FIG. 20 is a plan view of a handle substrate formed with the resistlayer;

FIG. 21 is a vertical sectional view of a modified example of thespectroscopic sensor of FIG. 1; and

FIG. 22 is a plan view of the cavity layer in the spectroscopic sensorof FIG. 20.

DESCRIPTION OF EMBODIMENTS

In the following, preferred embodiments of the present invention will beexplained in detail with reference to the drawings. In the drawings, thesame or equivalent parts will be referred to with the same signs whileomitting their overlapping descriptions.

As FIG. 1 illustrates, a spectroscopic sensor 1 comprises aninterference filter unit 20 for selectively transmitting therethroughlight in a predetermined wavelength range according to an incidentposition thereof, a light-transmitting substrate 3 for transmittingtherethrough the light incident on the interference filter unit 20, anda light-detecting substrate 4 for detecting the light transmittedthrough the interference filter unit 4. The spectroscopic sensor 1 isconstructed as a rectangular parallelepiped CSP (Chip Size Package) inwhich each side has a length of several hundred μm to several ten mm.

The light-transmitting substrate 3 is made of glass or the like andformed into a rectangular plate having a thickness on the order of 0.2to 2 mm. An optical filter layer 5 is formed on the rear face 3 b of thelight-transmitting substrate 3 so as to oppose the interference filterunit 20. The optical filter layer 5, which is a dielectric multilayerfilm or organic color filter (color resist), is formed into arectangular film having a thickness on the order of 0.1 to 10 μm. Theoptical filter layer 5 functions as a bandpass filter for transmittingtherethrough light in the predetermined wavelength range to be incidenton its opposed interference filter unit 20.

The light-detecting substrate 4, which is a photodiode array, is formedinto a rectangular plate having a thickness on the order of 10 to 150μm. The front face 4 a of the light-detecting substrate 4 is formed witha light-receiving unit 6 for receiving the light transmitted through theinterference filter unit 20. The light-receiving unit 6 is constructedby one-dimensionally arranging elongated photodiodes along thelongitudinal direction of the light-detecting substrate 4, while eachphotodiode extends along a direction substantially perpendicular to thelongitudinal direction of the light-detecting substrate 4. Thelight-detecting substrate 4 is further formed with leads 7 (frontwiring, back wiring, through wiring, etc.) for taking out electricsignals photoelectrically converted by the light-receiving unit 6. Therear face 4 b of the light-detecting substrate 4 is provided withsurface-mounting bumps 8 electrically connected to the leads 7. Thelight-detecting substrate 4 is not limited to a photodiode array, butmay also be any of other semiconductor light-detecting elements (C-MOSimage sensors, CCD image sensors, and the like).

The interference filter unit 20 has a cavity layer 21 and DBR(Distributed Bragg Reflector) layers 22, 23. In the interference filterunit 20, the DBR layers (first and second mirror layers) 22, 23 opposeeach other through the cavity layer 21. That is, the cavity layer 21keeps a distance between the DBR layers 22, 23 opposing each other. Eachof the DBR layers 22, 23 is a dielectric multilayer film made of SiO₂,TiO₂, Ta₂O₅, Nb₂O₅, Al₂O₃, MgF₂, or the like and formed into arectangular film having a thickness on the order of 0.1 to 10 μm.

The cavity layer 21 is a silicon oxide film (SiO₂ film), formed bythermally oxidizing silicon, having a thickness on the order of 100 nmto several μm. As FIGS. 1 and 2 illustrate, the cavity layer 21 has afilter region 24, a surrounding region 25, and a connecting region 26which are formed integrally.

The filter region 24 is formed into a rectangular film, in which eachside has a length on the order of several mm, and held between the DBRlayers 22, 23. More specifically, the DBR layer 22 is formed on thefront face 24 a of the filter region 24, while the DBR layer 23 isformed on the rear face 24 b of the filter region 24. The rear face 24 bof the filter region 24 is substantially parallel to a planeperpendicular to the incident direction of light (the direction in whichthe light-transmitting substrate 3 and the light-detecting substrate 4oppose each other), while the front face 24 a of the filter region 24 istilted with respect to this plane. As a consequence, the filter region24 gradually increases its thickness on the order of 100 nm to severalμm toward one longitudinal end of the spectroscopic sensor 1.

The surrounding region 25 is formed into a rectangular annular shape, inwhich each outer side has a length on the order of several mm, andsurrounds the filter region 24 with a predetermined distance d (e.g., onthe order of several μm to 1 mm) therefrom. The connecting region 26 isformed into a rectangular annular shape so as to be placed between thefilter region 24 and surrounding region 25 and connects an end part 24 eof the filter region 24 on the light-detecting substrate 4 side and anend part 25 e of the surrounding region 25 on the light-detectingsubstrate 4 side to each other. The filter region 24, surrounding region25, and connecting region 26 form a groove G which extends such as tosurround the filter region 24 with a width d in the cavity layer 21.

As FIG. 1 illustrates, the front face (end face on thelight-transmitting substrate side) 25 a of the surrounding region 25 hassubstantially the same height as with a part 24 h located closest to thelight-transmitting substrate 3 in the front face (first mirror layerforming surface) 24 a of the filter region 24 or is positioned nearer tothe light-transmitting substrate 3 than is this part 24 h. The frontface (end face on the light-transmitting substrate side) 26 a of theconnecting region 26 has substantially the same height as with a part 24l located closest to the light-detecting substrate 4 in the front face24 a of the filter region 24 or is positioned nearer to thelight-detecting substrate 4 than is this part 24 l. On the other hand,the rear face 24 b of the filter region 24, the rear face 25 b of thesurrounding region 25, and the rear face 26 b of the connecting region26 are substantially flush with each other. Here, a side face 25 c ofthe surrounding region 25 is flush with a side face 3 c of thelight-transmitting substrate 3 and a side face 4 c of thelight-detecting substrate 4. However, a gap on the order of 0 to 100 μmmay occur between the side face 3 c of the light-transmitting substrate3 and the side face 4 c of the light-detecting substrate 4.

The light-transmitting substrate 3 is arranged on the DBR layer 22 sideof the cavity layer 21 and joined to the cavity layer 21 and DBR layer22 through a coupling layer (first coupling layer) 11. Thelight-detecting substrate 4 is arranged on the DBR layer 23 side of thecavity layer 21 and joined to the cavity layer 21 and DBR layer 23through a coupling layer (second coupling layer) 12. Each of thecoupling layers 11, 12 arranged between the interference filter unit 20and the light-transmitting substrate 3 and light-detecting substrate 4is a silicon oxide film formed by a film forming process using TEOS(Tetraethyl Orthosilicate, Tetraethoxysilane) as a material gas and hasa thickness on the order of several hundred nm to 10 μm.

In thus constructed spectroscopic sensor 1, when light incident on thelight-transmitting substrate 3 from the front face 3 a thereof passestherethrough to reach the rear face 3 b thereof, only light in apredetermined wavelength range to be incident on the interference filterunit 20 is transmitted through the optical filter layer 5. Then, whenthe light transmitted through the optical filter layer 5 is incident onthe interference filter unit 20, light in a predetermined wavelengthrange is selectively transmitted therethrough according to its incidentposition. That is, a wavelength of light to enter each channel of thelight-receiving unit 6 of the light-detecting substrate 4 is uniquelydetermined by the thicknesses and kinds of the DBR layers 22, 23 andthickness of the cavity layer 21 at the incident position. As aconsequence, light having a different wavelength is detected for eachchannel of the light-receiving unit 6 in the light-detecting substrate4.

In the spectroscopic sensor 1, as explained in the foregoing, the cavitylayer 21 is a silicon oxide film and thus can stabilize its form, lighttransmittance, refractive index, and the like more than when made of aresin material. The coupling layers 11, 12 are silicon oxide films andthus can stabilize the transmission characteristic of the lightadvancing from the light-transmitting substrate 3 to the interferencefilter unit 20 and that of the light progressing from the interferencefilter unit 20 to the light-detecting substrate 4 more than when made ofresin materials. The fact that the cavity layer 21 and coupling layers11, 12 are silicon oxide films can also prevent their quality from beingdegraded by changes in temperature, high humidity, and the like of theenvironment where they are in use. Specifically, the cavity layer 21 andcoupling layers 11, 12 can prevent moisture absorption which may occurif they are made of resin materials, while suppressing thermal expansionand contraction more, so as to become more thermally stable, than whenmade of resin materials. Therefore, the spectroscopic sensor 1 becomesextremely reliable.

The cavity layer 21 is a silicon oxide film formed by thermallyoxidizing silicon. This stably yields the cavity layer 21 with highquality at low cost.

The coupling layers 11, 12 are silicon oxide films formed by a filmforming process using TEOS as a material gas. This can form the couplinglayers 11, 12 at low temperature and high speed with low stress, so asto prevent the cavity layer 21 and DBR layers 22, 23 from being damaged,whereby the cavity layer 21 and DBR layers 22, 23 are obtained with highquality.

The optical filter layer 5 is formed on the light-transmitting substrate3 so as to oppose the DBR layer 22. This allows light in a predeterminedwavelength to become efficiently incident on the interference filterunit 20.

Additionally, in the spectroscopic sensor 11, the filter region 24 issurrounded by the surrounding region 25 with the predetermined distanced therebetween in the cavity layer 21, while the end part 24 e of thefilter region 24 and the end part 25 e of the surrounding region 25 areconnected to each other by the connecting region 26. As a consequence,any external force acting in a direction perpendicular to the directionin which the light-transmitting substrate 3 and light-detectingsubstrate 4 oppose each other is buffered by the surrounding region 25and connecting region 26, whereby the filter region 24 can be preventedfrom being damaged.

The front face 25 a of the surrounding region 25 has substantially thesame height as with the part 24 h located closest to thelight-transmitting substrate 3 in the front face 24 a of the filterregion 24 or is positioned nearer to the light-transmitting substrate 3than is this part 24 h. As a consequence, any external force acting in adirection parallel to the direction in which the light-transmittingsubstrate 3 and light-detecting substrate 4 oppose each other (e,g., anexternal force applied upon direct bonding between coupling layers 11 a,11 b or 12 a, 12 b which will be explained later) can be received by thesurrounding region 25, so as to be prevented from damaging the filterregion 24.

The front face 26 a of the connecting region 26 has substantially thesame height as with the part 24 l located closest to the light-detectingsubstrate 4 in the front face 24 a of the filter region 24 or positionednearer to the light-detecting substrate 4 than is this part 24 l. As aconsequence, any external force acting in a direction perpendicular tothe direction in which the light-transmitting substrate 3 andlight-detecting substrate 4 oppose each other can be prevented frombeing directly exerted on the front face 24 a of the filter region 24,which is a surface for forming the DBR layer 22.

A method for manufacturing the above-mentioned spectroscopic sensor 1will now be explained. First, as FIG. 3 illustrates, one main face 50 aof a silicon substrate 50 and the other main face 50 b thereof arethermally oxidized, so as to form silicon oxide films 52 on one mainface 51 a of a handle substrate 51 made of silicon and the other mainface 51 b thereof, and the silicon oxide film 52 formed on the one mainface 51 a or other main face 51 b of the handle substrate 51 is employedas a surface layer 53. Here, the silicon oxide film 52 formed on the onemain face 51 a of the handle substrate 51 is employed as the surfacelayer 53. The surface layer 53 has a thickness of about 1000 nm.

Subsequently, as FIGS. 4 and 5 illustrate, a resist layer 54 for etchingto produce a plurality of cavity layers 21 arranged in a matrix isformed on the surface layer 53. Then, using the resist layer 54 as amask, the surface layer 53 provided on the handle substrate 51 is etched(etched back), so as to form a plurality of cavity layers 21 arranged ina matrix (first step).

Next, as FIG. 6 illustrates, the DBR layer 22 is formed on the cavitylayer 21 for each part corresponding to one spectroscopic sensor 1(second step). For forming the DBR layer 22, film forming by ionplating, vapor deposition, sputtering, or the like and patterning byphotoetching and liftoff or etching are performed. Since onespectroscopic sensor 1 is provided with one cavity layer 21 here, whenforming the DBR layer 22, the film forming may be performed on the wholesurface so as to cover all the cavity layers 21 instead of patterningeach part corresponding to one spectroscopic sensor 1. Subsequently, asFIG. 7 illustrates, a silicon oxide film is formed on the cavity film 21such as to cover the DBR layer 22 by a film forming process using TEOSas a material gas, and its surface is flattened by CMP (ChemicalMechanical Polishing), thus forming the coupling layer 11 a.

The film forming process using TEOS as a material gas enables filmforming at low temperature (e.g., at a film forming temperature of 200°C. or lower) and high speed with low stress by plasma CVD, LP-CVD,AP-CVD, or the like. In the plasma CVD, TEOS is supplied by bubblingwith an He gas, heating with a heater, or the like and caused togenerate a plasma-assisted decomposition reaction within a chamber, soas to react with an O₂ gas, thereby forming the silicon oxide film.

On the other hand, as FIG. 8 illustrates, a light-transmitting wafer 30including a plurality of light-transmitting substrates 3 arranged in amatrix is prepared, and the optical filter layer 5 is formed for eachpart corresponding to the light-transmitting substrate 3 on thelight-transmitting wafer 30 (i.e., on the light-transmitting substrate3). When forming the optical filter layer 5 from a dielectric multilayerfilm, film forming by ion plating, vapor deposition, sputtering, or thelike and patterning by photoetching and liftoff or etching areperformed. When forming from an organic color filter, the optical filterlayer 5 is patterned by exposure and development or the like as with aphotoresist. Since one spectroscopic sensor 1 is provided with oneoptical filter layer 5 here, when forming the optical filter layer 5,the film forming may be performed on the whole surface so as to coverall the light-transmitting wafer 30 instead of patterning each partcorresponding to one spectroscopic sensor 1. Subsequently, as FIG. 9illustrates, a silicon oxide film is formed on the light-transmittingwafer 30 such as to cover the optical filter layer 5 by a film formingprocess using TEOS as a material gas, and its surface is flattened byCMP, thus forming the coupling layer 11 b.

Next, as FIGS. 10 and 11 illustrate, the DBR layer 22 and the opticalfilter layer 5 are caused to oppose each other for each partcorresponding to one spectroscopic sensor 1, and the respective surfacesof the coupling layers 11 a, 11 b are directly bonded (e.g., bysurface-activated bonding) to each other, thus joining the handlesubstrate 51 and the light-transmitting wafer 30 to each other (thirdstep). That is, the light-transmitting substrate 3 is joined onto theDBR layer 22 such that the DBR layer 22 and the optical filter layer 5oppose each other through the coupling layer 11. When the optical filterlayer 5 is not formed on the light-transmitting wafer 30, the couplinglayer 11 b as a flattening layer is unnecessary.

Subsequently, as FIG. 12 illustrates, the silicon oxide film 52 formedon the other main face 51 b of the handle substrate 51 and a part of thehandle substrate 51 on the other main face 51 b side are ground, so thatthe handle substrate 51 becomes thinner. Then, as FIG. 13 illustrates,the handle substrate 51 is wet- or dry-etched, so as to remove thehandle substrate 51 from the cavity layer 21 (fourth step). Here, thesilicon oxide film 52 formed on the other main face 51 b of the handlesubstrate 51 and the handle substrate 51 may be removed by wet or dryetching without grinding.

Next, as FIG. 14 illustrates, the DBR layer 23 is formed in the samemanner as with the DBR layer 22 on the cavity layer 21 exposed byremoving the handle substrate 51 (fifth step). As a consequence, foreach part corresponding to one spectroscopic sensor 1, the DBR layers22, 23 oppose each other through the cavity layer 21, thereby formingthe interference filter unit 20. Then, a part corresponding to onespectroscopic sensor 1 becomes a spectroscopic filter substrate 9,whereby a spectroscopic filter wafer 90 including a plurality ofspectroscopic filter substrates 9 arranged in a matrix is produced.Since one spectroscopic sensor 1 is provided with one cavity layer 21here, when forming the DBR layer 23, the film forming may be performedon the whole surface so as to cover all the cavity layers 21 instead ofpatterning each part corresponding to one spectroscopic sensor 1.

Thereafter, as FIG. 15 illustrates, a silicon oxide film is formed onthe cavity layer 21 such as to cover the DBR 23 by a film formingprocess using TEOS as a material gas, and its surface is flattened byCMP, thus forming the coupling layer 12 a. On the other hand, as FIG. 16illustrates, a light-detecting wafer 40 including a plurality oflight-detecting substrates 4 is prepared. Then, a silicon oxide film isformed on the light-detecting wafer 40 such as to cover thelight-receiving units 6 by a film forming process using TEOS as amaterial gas, and its surface is flattened by CMP, thus forming thecoupling layer 12 b.

Next, as FIGS. 16 and 17 illustrate, the DBR layer 23 and thelight-receiving unit 6 are caused to oppose each other for each partcorresponding to one spectroscopic sensor 1, and the respective surfacesof the coupling layers 12 a, 12 b are directly bonded to each other,thus joining the spectroscopic filter wafer 90 and the light-detectingwafer 40 to each other (sixth step). That is, the light-detectingsubstrate 4 is joined onto the DBR layer 23 such that the DBR layer 23and the light-receiving unit 6 oppose each other through the couplinglayer 12.

Subsequently, as FIG. 18 illustrates, the rear face of thelight-detecting wafer 40 is ground, polished, etched, and so forth, suchthat the light-detecting wafer 40 is thinned to a thickness on the orderof 10 to 150 μm. Then, a through-hole is formed by etching in a partcorresponding to front wiring, and through wiring, back wiring, and thelike are formed, so as to produce the lead 7 for each part correspondingto one spectroscopic sensor 1. Further, the bump 8 is formed on the rearface of the light-detecting wafer 40 for each part corresponding to onespectroscopic sensor 1. Finally, the spectroscopic filter wafer 90 andlight-detecting wafer 40 joined to each other are diced into each partcorresponding to one spectroscopic sensor 1, so as to yield a pluralityof spectroscopic sensors 1. Pad parts such as the front wiring and backwiring constituting the leads 7 may be not only embedded in the frontand rear faces of the light-detecting wafer 40 (i.e., light-detectingsubstrate 4), but also disposed thereon so as to project therefrom bytheir thickness, for example.

As explained in the foregoing, the method for manufacturing thespectroscopic sensor 1 forms the cavity layer 21 by etching the surfacelayer 53 disposed on the handle substrate 51. Thus forming the cavitylayer 21 by etching with the handle substrate 51 can stably yield thecavity layer 21 with a high precision. Further, after forming the cavitylayer 21 and DBR layers 22, 23 on the light-transmitting substrate 3side, the light-detecting substrate 4 is joined thereto. This canprevent the light-detecting substrate 4 from being damaged in theprocesses for forming the cavity layer 21 and DBR layers 22, 23. Hence,this method for manufacturing the spectroscopic sensor 1 can yield thehighly reliable spectroscopic sensor 1.

Since the spectroscopic filter wafer 90 and the light-detecting wafer 40are joined to each other after inspecting performances of eachspectroscopic filter substrate 9 in the spectroscopic filter wafer 90,the light-detecting wafer 40 can be prevented from being wasted becauseof failures on the spectroscopic filter wafer 90 side.

Since the silicon oxide film 52 formed on one main face 51 a of thehandle substrate 51 made of silicon is employed as the surface layer 53,the cavity layer 21 can stably be obtained at low cost with highquality. Also, since both main faces 50 a, 50 b of the silicon substrate50 are thermally oxidized so as to form the silicon oxide films 52 onboth main faces of the handle substrate 51 made of silicon, the handlesubstrate 51 is restrained from waiving. Hence, the cavity layer 21 canstably be obtained with a high precision.

The optical filter layer 5 is formed on the light-transmitting substrate3, and then the light-transmitting substrate 3 is joined onto the DBRlayer 22 such that the DBR layer 22 and the optical filter layer 5oppose each other. This can make light in a predetermined wavelengthrange efficiently incident on the interference filter unit 20.

When etching the surface layer 53 disposed on the handle substrate 51while using the resist layer 54 as a mask, a part corresponding to thegroove G in the resist layer 54 is removed in advance, so that a partcorresponding to the groove G in the surface layer 53 is exposed atfirst. When the part corresponding to the groove G in the surface layer53 is exposed, oxygen breaks away from the surface layer 53 made ofSiO₂, so as to work as an etchant for the resist layer 54. Here, thepart corresponding to the groove G in the surface layer 53 surrounds thepart corresponding to the filter region 24 in the surface layer 53.Therefore, the whole part corresponding to the filter region 24 in thesurface layer 53 is stably fed with oxygen and, as a result, reliablyetched.

Without such oxygen supply, the etchant density distribution is likelyto be biased by a loading effect and the like (e.g., the etchant issupplied more and less in the peripheral and center parts of the handlesubstrate 51, respectively), so that the form of the filter region 24produced by etching may vary depending on locations in the handlesubstrate 51. In particular, when the resist layer 54 is made of anorganic material, the etching rate varies greatly depending on the stateof supplying oxygen as the etchant, whereby the above-mentioned supplyof oxygen is very important.

When dicing the spectroscopic filter wafer 90 and light-detecting wafer40 joined to each other into each part corresponding to onespectroscopic sensor 1, chipping and the like can be prevented fromoccurring, since the spectroscopic filter wafer 90 and light-detectingwafer 40 are firmly integrated together as a whole by direct bondingbetween the coupling layers 11 a, 11 b and between the coupling layers12 a, 12 b.

The relationship between the resist layer 54 and the cavity layer 21will now be explained. As FIG. 19 illustrates, the resist layer 54 isformed on a flat surface (see a solid line in FIG. 19) of the cavitylayer 21 before etching (i.e., the surface layer 53). The resist layer54 has a three-dimensional form corresponding to the shape of the cavitylayer 21 to be formed (i.e., the cavity layer 21 after etching). Such aresist layer 54 can be formed by utilizing a photomask whosetransmittance is adjusted according to locations, photolithography or EBlithography whose amount of dose is adjusted according to locations,nanoimprinting, and the like.

When performing etch back (i.e., whole surface etching) based on theform of the resist layer 54, the etching rate for the resist layer 54and cavity layer 21 may be adjusted depending on etching conditions.This can produce various forms of cavity layers 21 from the resist layer54 having one kind of form. In the case illustrated in FIG. 19, theetching rate for the resist layer 54 is about twice as fast as that forthe cavity layer 21, so that the inclination of the surface of thecavity layer 21 after etching (see a dash-single-dot line in FIG. 19) ismilder than that of the surface of the resist layer 54 (see a brokenline in FIG. 19).

A monitor pattern disposed on the handle substrate 51 will now beexplained. While the surface layer 53 is formed by a substantiallyconstant thickness on the handle substrate 51 as FIG. 4 illustrates, notonly the resist layer 54 for forming a plurality of cavity layers 21 byetching, but resist layers 55 as a monitor pattern are also formed onthe surface layer 53 as FIG. 20 illustrates. The resist layers 54, 55are integrally formed by utilizing the photomask, photolithography or EBlithography, nanoimprinting, and the like as mentioned above.

The resist layers 55 as a monitor pattern are grouped by a plural number(9 here), and the resulting groups are arranged at a plurality oflocations (4 peripheral locations and 1 center location here) on thehandle substrate 51. Each of the grouped resist layers 55 is formed by asubstantially constant thickness corresponding to its corresponding oneof a plurality of parts of one resist layer 54. For example, the groupedresist layers 55 have the thickness of a predetermined part of theresist layer 54 corresponding to a predetermined part of the filterregion 24, the thickness of a predetermined part of the resist layer 54corresponding to a predetermined part of the surrounding region 25, andthe thickness of a predetermined part of the resist layer 54corresponding to a predetermined part of the connecting region 26 (i.e.,the bottom face of the groove G).

As a consequence, measuring the thickness of the surface layer 53 in apart stripped of the resist layer 55 as a monitor pattern with anoptical thickness meter at a predetermined timing such as that in themiddle of etching the surface layer 53 or after the completion thereofcan acquire the thickness of a predetermined part of the cavity layer 21corresponding thereto. When the measurement timing is in the middle ofetching the surface layer 53, at which the resist layer 54 remains in apredetermined part of the cavity layer 21, the thickness of the resistlayer 54 remaining in this part can be acquired by the same method.

Thus utilizing the resist layer 55 as a monitor pattern is veryeffective, since each cavity layer 21 is small, while the surface 24 aof the filter region 24 is tilted, so that the thickness of the cavitylayer 21 is hard to measure directly with an optical thickness meter.Further, since the resist layers 55 as a monitor pattern are arranged ata plurality of locations on the handle substrate 51, how the etchingprogresses (progress distribution) in the whole surface layer 53 on thehandle substrate 51 can be evaluated.

The thickness of the cavity layer 21 corresponding to a predeterminedpart of the filter region 24 can also be acquired in the followingmanner. That is, the difference in level between the surface of thecavity layer 21 corresponding to the predetermined part of the filterregion 24 and the bottom face of the groove G is measured by an AFM(Atomic Force Microscope), a step gauge of a probe type, or the like ata predetermined timing such as that in the middle of etching the surfacelayer 53 or after the completion thereof. On the other hand, in a partstripped of the resist layer 55 as a monitor pattern corresponding tothe bottom face of the groove G, the thickness of the surface layer 53is measured by an optical thickness meter. Then, the difference in levelbetween the surface of the cavity layer 21 and the bottom face of thegroove G is added to the thickness of the surface layer 53 as measured,so as to compute the thickness of the cavity layer 21 corresponding tothe predetermined part of the filter region 24. When the measurementtiming is in the middle of etching the surface layer 53, at which theresist layer 54 remains in a part corresponding to the predeterminedpart of the cavity layer 21, the thickness of the resist layer 54remaining in this part can be acquired by the same method.

While an embodiment of the present invention is explained in theforegoing, the present invention is not limited thereto. For example,various materials and forms may be employed for constituent members ofthe spectroscopic sensor without being limited to those mentioned above.

The spectroscopic sensor may comprise a plurality of interference filterunits for selectively transmitting therethrough light in a predeterminedwavelength range according to an incident position thereof. Aspectroscopic sensor comprising a plurality of interference filter unitswill now be explained. As FIG. 21 illustrates, this spectroscopic sensor1 comprises a plurality of interference filter units 20A, 20B. Theinterference filter units 20A, 20B are arranged in a row longitudinallyof the spectroscopic sensor 1 between the light-transmitting substrate 3and the light-detecting substrate 4.

In the cavity layer 21, as FIGS. 21 and 22 illustrate, filter regions 24formed for the interference filter units 20A, 20B, respectively, arejuxtaposed to each other, while each filter region 24 is held betweenDBR layers 22, 23. A surrounding region 25 surrounds the juxtaposedfilter regions 24, 24 with a predetermined distance d therefrom whenseen in the incident direction of light. A connecting region 26 connectsan end part on the light-detecting substrate 4 side of the juxtaposedfilter regions 24, 24 and an end part on the light-detecting substrate 4side of the surrounding region 25 to each other.

The respective DBR layers 22 for the interference filter units 20A, 20Bdiffer from each other in their kinds, and their boundaries may overlapeach other partly, be in contact with each other with no gaptherebetween, or be separated from each other by a gap of about 5 μm,for example. The respective DBR layers 23 for the interference filterunits 20A, 20B differ from each other in their kinds, and theirboundaries may overlap each other partly, be in contact with each otherwith no gap therebetween, or be separated from each other by a gap ofabout 5 μm, for example. Examples of the two DBR layers different fromeach other in their kinds include films constituted by differentmaterials and (single-layer or multilayer) films made of the samematerials with different thicknesses. The respective optical filterlayers 5 for the interference filter units 20A, 20B differ from eachother in their kinds, and their boundaries may overlap each otherpartly, be in contact with each other with no gap therebetween, or beseparated from each other by a gap of about 5 μm, for example.

In thus constructed spectroscopic sensor 1, when light incident on thelight-transmitting substrate 3 from the front face 3 a thereof passesthrough the light-transmitting substrate 3 and reaches the rear face 3 bthereof, only light in a predetermined wavelength range to be incidenton the interference filter units 20A, 20B is transmitted through theoptical filter layer 5. When the light transmitted through the opticalfilter layer 5 is incident on any of the interference filter units 20A,20B, light in a predetermined wavelength range selectively passestherethrough according to its incident position. That is, a wavelengthof light to enter each channel of the light-receiving unit 6 of thelight-detecting substrate 4 is uniquely determined by the thicknessesand kinds of the DBR layers 22, 23 and thickness of the cavity layer 21at the incident position. As a consequence, light having a differentwavelength is detected for each channel of the light-receiving unit 6 inthe light-detecting substrate 4.

Colored glass or filter glass which transmits therethrough light in apredetermined wavelength range may also be used as a material for thelight-transmitting substrate 3. Another optical filter layer may beformed on the front face 3 a of the light-transmitting substrate 3 inaddition to or in place of the optical filter layer 5. Thelight-detecting substrate 4 is not limited to the one-dimensionalsensor, but may be a two-dimensional sensor. The thickness of the cavitylayer 21 may vary two-dimensionally or stepwise. A single-layerreflective metal film of AL, Au, Ag, or the like may be used as a mirrorlayer in place of the DBR layers 22, 23. The spectroscopic sensor mayalso be constructed as an SMD (Surface Mount Device) instead of a CSP.

The coupling layers 11, 12 may also be silicon oxide films formed byplasma CVD using a silane gas, coating type SOG (Spin On Glass), vapordeposition, sputtering, or the like. Joining through an optical resinlayer or at an outer edge part of the spectroscopic sensor 1 may beemployed in place of the joining through the coupling layers 11, 12(i.e., direct bonding). The joining through the optical resin layer mayuse any of optical resins such as organic materials based on epoxy,acrylic, and silicone and hybrid materials made of organic and inorganicsubstances as a material for the optical resin layer. The joining at theouter edge part of the spectroscopic sensor 1 can be achieved bylow-melting glass, solder, or the like while keeping a gap with aspacer. In this case, the region surrounded by the joint may be left asan air gap or filled with an optical resin.

A silicon oxide film may be formed on one main face of the handlesubstrate made of silicon by a film forming process using TEOS as amaterial gas, plasma CVD using a silane gas, coating type SOG, vapordeposition, sputtering, LP-CVD, or the like and employed as a surfacelayer. Silicon oxide films may be formed on both main faces of thehandle substrate made of silicon by LP-CVD instead of thermaloxidization, and the silicon oxide film formed on one of the main facesof the handle substrate may be used as a surface layer. That is, thecavity layer that is a silicon oxide film is not limited to the oneformed by thermally oxidizing silicon. However, forming the siliconoxide film by thermal oxidization has merits in that the cavity layerbecomes a denser film, has better uniformity in thickness, incurssmaller amounts of impurities, and exhibits more stable opticalcharacteristics such as transmittance and refractive index than whenmade by the other methods mentioned above.

INDUSTRIAL APPLICABILITY

The present invention can provide a highly reliable spectroscopicsensor.

REFERENCE SIGNS LIST

1 . . . spectroscopic sensor; 3 . . . light-transmitting substrate; 4 .. . light-detecting substrate; 5 . . . optical filter layer; 11 . . .coupling layer (first coupling layer); 12 . . . coupling layer (secondcoupling layer); 20, 20A, 20B . . . interference filter unit; 21 . . .cavity layer; 22 . . . DBR layer (first mirror layer); 23 . . . DBRlayer (second mirror layer)

The invention claimed is:
 1. A spectroscopic sensor comprising: aninterference filter unit, having a cavity layer and first and secondmirror layers opposing each other through the cavity layer, forselectively transmitting therethrough light in a predeterminedwavelength range according to an incident position thereof; alight-transmitting substrate, arranged on the first mirror layer side,for transmitting therethrough light incident on the interference filterunit; a light-detecting substrate, arranged on the second mirror layerside, for detecting the light transmitted through the interferencefilter unit; and a first coupling layer arranged between theinterference filter unit and the light-transmitting substrate; whereinthe cavity layer and the first coupling layer are silicon oxide films,the thickness of the cavity layer varies between the first and secondmirror layers, the thickness of the first coupling layer varies suchthat the light-transmitting substrate and the light-detecting substrateare arranged parallel to each other, the cavity layer has a filterregion held between the first and second mirror layers, and asurrounding region continuously surrounding the whole perimeter of thefilter region as seen in a direction in which the light-transmittingsubstrate and the light-detecting substrate oppose each other, thecavity layer is formed continuously over the filter region and thesurrounding region, an entire face on the light-transmitting substrateside of the surrounding region has substantially the same height as apart of a face of the filter region on which the first mirror layer isformed located closest to the light-transmitting substrate or the entireface on the light-transmitting substrate side of the surrounding regionis positioned nearer to the light-transmitting substrate than the part,the filter region overlaps with a light-receiving unit of thelight-detecting substrate and the surrounding region does not overlapwith the light-receiving unit as seen in the direction in which thelight-transmitting substrate and the light-detecting substrate opposeeach other, and the thickness of the filter region varies between thefirst and second mirror layers.
 2. A spectroscopic sensor according toclaim 1, further comprising a second coupling layer arranged between theinterference filter unit and the light-detecting substrate; wherein thesecond coupling layer is a silicon oxide film.
 3. A spectroscopic sensoraccording to claim 1, further comprising an optical filter layer, formedon the light-transmitting substrate so as to oppose the first mirrorlayer, for transmitting therethrough light in the predeterminedwavelength range.
 4. A method for manufacturing a spectroscopic sensoraccording to claim 1, the method comprising: a step of forming thecavity layer made of a silicon oxide film; a step of forming the firstmirror layer on the cavity layer; a step of joining thelight-transmitting substrate on the first mirror layer via the firstcoupling layer made of a silicon oxide film a step of forming the secondmirror layer on the cavity layer; and a step of joining thelight-detecting substrate on the second mirror layer via a secondcoupling layer made of a silicon oxide film.
 5. A method formanufacturing a spectroscopic sensor according to claim 4, wherein, thestep of forming the cavity layer forms the cavity layer made of thesilicon oxide film by thermally oxidizing silicon.
 6. A method formanufacturing a spectroscopic sensor according to claim 4, wherein, thestep of joining the light-transmitting substrate forms the firstcoupling layer made of the silicon oxide film by a film forming processusing TEOS as a material gas.
 7. A method for manufacturing aspectroscopic sensor according to claim 4, wherein, the step of joiningthe light-detecting substrate forms the second coupling layer made ofthe silicon oxide film by a film forming process using TEOS as amaterial gas.